Had to be Lee Pace as Ned -- even though he's not really new to TV. Anyone but me remember Wonderfalls? He played the older brother... a character that was supposed to be older than he (actually) is even now.

people are saying that Blair just arrived (sorry, her ral name is just whatever), but she wa sin 24 and some other shows i can't remember. when i first saw GG i knew Blair already. so she's also not break-out if you apply the same standarts as to Blake. Blake was only in Sisterhood (which I love, mostly because of Alexis, by the by where is she? she's amazing).

I dont watch any of these shows lol so I wouldnt know .. but Chyler Leigh of Grey's Anatomy is one of my new favorites to the cast, she has somewhat of a history not so much a breaking out but still this is the first role I would have recognized her for.

They're all great, and my crush on Lee Pace gets bigger with every Pushing Daisies episode, but his character doesn't quite "breakout". Olive and Emerson Cod totally steals that show.
Leighton Meester as Blair is more of a breakout star. Gossip Girl wouldn't be nearly as good without her very compelling mix of bitchiness and fragile vulnerability. Not to mention the way she just exudes old-world glamour (even when she's wearing bright colored tights and ridiculously huge bows!)